This project has focused upon the role of prostaglandins, particularly prostacyclin in the regulation of vascular functions in both the hypertensive rat (SHR) and experimentally-induced rat with diabetes mellitus(alloxan). Changes in reactivity of isolated vascular smooth muscle have been demonstrated, there being a general tendency toward an enhanced reactivity of diabetic tissues. Observations on venous segments also suggest an alteration in the contractility mechanisms in the diabetic state. In the hypertensive state, attention has been directed towards the effect of in vivo antihypertensive activity on in vitro reactivity of arterial tissue, when treated with various agonists such as high concentrations of certain prostaglandins.